The invention is directed to a process and apparatus for the pyrolytic decomposition of organic materials, particularly radioactively contaminated organic materials, containing a halogen (Cl, Br, F, I) and/or phosphorus at 300.degree. to 800.degree. C. in a reactor.
In the nuclear art there are a number of contaminated organic solvent and extraction agents which must be removed.
The chief amount of contaminated organic materials which must be removed consists of a mixture of tributyl phosphate (TBP) and kerosene, which for example is employed in the volume ratio 30:70 as extraction agent in the reprocessing of spent fuel elements according to the PUREX process.
At other places in the nuclear art, e.g. in the organic conversion of UF.sub.6 to UF.sub.4 perchloroethylene is obtained as waste in admixture with partially fluorinated products, which likewise must be eliminated.
However, also in the conventional area there are wastes of fluorinated, chlorinated and phosphorus containing solvents which cannot be burned without problems or, if they are not burnable, cannot by pyrolyzed without problem, since in this case, especially in the hot, they develop extraordinarily corrosive and environmentally undesirably acting phosphoric acid, hydrogen chloride and hydrogen fluoride.
In the conventional area the elimination of these materials generally take place in an environmentally undesirable manner by burning on combustion ships on the high seas. In the case of radioactively contaminated waste from the point of view of the political environmental burning on the high seas is essentially intolerable.
Therefore waste from the nuclear art must be conveyed with substantially stronger safety precautions into the final storable condition. There are included in these safety precautions that the waste on the one hand must be reduced to the smallest possible volume and on the other hand that the process for the reduction operates with high decontamination factors and the smallest possible secondary waste. The waste occurring in the nuclear art of the categories considered consists essentially of TBP/kerosene.
Several processes or process variants are described and have been listed especially for removal of TBP/kerosene.
It is disadvantageous that in the burning on the one hand P.sub.2 O.sub.5, which is a glass former, forms and very quickly leads to clogging in the waste gas system of the combustion plant through the formation of phosphate glasses. On the other hand in the middle temperature range by reaction with the water of reduction that arises, it forms phosphoric acid which because of its extraordinary corrosiveness causes damage to metallic parts of the plants (W. Bahr, W. Hempelmann and H. Krause, KfK-2418, February 1977).
Furthermore there was tried burning in a Na.sub.2 CO.sub.3 melt for the removal of TBP or TBP/kerosene mixture. Hereby there takes place an in situ neutralization of the P.sub.2 O.sub.5 or phosphoric acid. However, there forms high melting metaphosphate which can lead to handling problems (D. L. Ziegler, A. J. Johnson, Proceedings 14th ERDA Air Cleaning Conference, February 1977).
In British patent No. 1517014 there is described a process for handling contaminated TBP/kerosene wastes in which first the TBP is separated from kerosene with phosphoric acid and then the adduct formed is thermally decomposed at about 200.degree. C. to phosphoric acid and butene. The butene is burned, the highly active phosphoric acid precipitated with calcium hydroxide and the calcium phosphate formed conveyed to final storage. The additional introduction into the process of phosphoric acid which is necessary for the formation of adduct produces additional secondary waste which is a particular disadvantage of this process.
Besides there is described a process (German OS No. 2855650 and related Vietzke U.S. application Ser. No. 104,736 filed Dec. 19, 1979, the entire disclosure of which is hereby incorporated by reference and relied upon), a process in which the TBP/kerosene mixture is reacted in a fluidized bed which uses the simultaneous presence of a basic granulate as fluidized material. Hereby there takes place reaction of the TBP to phosphoric acid and a mixture of butene and butanol. Kerosene distills off and in the presence of excess warm steam can be burned together with the butene and butanol. The phosphoric acid is bound through the basic materials, preferably CaO or Ca(OH).sub.2, present as the fluidizing material, as insoluble phosphates which are drawn off from the fluidized bed reactor and are conveyed to the final storage. Certainly in a fluidized bed normally there is needed an increased amount of reaction gas which leads to an increased amount of waste gas and to development of dust in the reaction space, which can have a significant influence on the stream time of the filter candles at the outlet of the reactor. Besides there is produced radioactively contaminated water which must be worked up in an additional process step.
Therefore it was the problem of the present invention to develop a process and an apparatus for the pyrolytic decomposition of halogen (i.e. Cl, Br, F, or I) and/or phosphorus containing organic materials, especially radioactively contaminated organic materials, at 300.degree. to 800.degree. C. in a reactor so that all mixtures of organic materials can be worked up without formation of corrosive, secondary products, at minimal amounts of waste gas, low dust development in the reactor and simultaneously high decontamination factors. Furthermore, as residue in the reactor, there should be obtained the most inert inorganic product possible, preferably readily conditionable in cement.